Drugs and pharmaceutical agents are delivered to patients by a variety of methods. A typical method delivers the drug or pharmaceutical agent subcutaneously by a stainless steel cannula. Although the subcutaneous sampling and delivery methods using a cannula are effective for many applications, the pain normally induced by the cannula has prompted the development of less painful delivery methods.
The skin is made up of several layers, with the upper composite layer being the epithelial layer. The outermost layer of the skin, the stratum corneum, is a waterproof membrane with well known barrier properties that prevent the influx of undesirable molecules and various foreign substances while preventing the outflux of various analytes. The stratum corneum is a complex structure of compacted keratinized cell remnants having a thickness of about 10–30 microns.
The natural impermeability of the stratum corneum prevents the administration of most pharmaceutical agents and other substances through the skin. Numerous methods and devices have been proposed to enhance the permeability of the skin and to increase the diffusion of various drugs through the skin for utilization by the body. Typically, the delivery of drugs through the skin is enhanced by increasing either the permeability of the skin or the force or energy used to direct the drug through the skin.
Another method of sampling and delivering various substances through the skin is by forming micropores or cuts through the stratum corneum. By piercing the stratum corneum and delivering a drug to the skin in or below the stratum corneum, many drugs can be administered effectively. In a similar manner, some substances can be extracted from the body through cuts or pores formed in the stratum corneum. The devices for piercing the stratum corneum generally include a plurality of micron size needles or blades having a length to pierce the stratum corneum without passing completely through the epidermis. Examples of these devices are disclosed in U.S. Pat. No. 5,879,326 to Godshall et al.; U.S. Pat. No. 5,250,023 to Lee et al., and WO 97/48440.
The above-noted devices that include micron-sized needles or blades can be effective in delivering substances to the body. However, these needles and blades having a length of a few microns to a few hundred microns typically do not penetrate skin to a uniform depth. The natural elasticity and resilience of the skin will often result in the skin being deformed by the needles rather than pierced. A microneedle array when pressed against the skin often results in the outermost needles penetrating the skin while the innermost needles do not penetrate or only penetrate to depth less than the outermost needles.
The prior methods and devices for the intradermal administration of substances have exhibited limited success. Accordingly, an unmet need exists in the industry for an improved device for the sampling and administration of various drugs and other substances to the body.